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Satellite sees extent of Mideast floods.

A new technique for measuring soil wetness from space shows that flooding in the Midwest has spread far beyond the immediate vicinity of the Mississippi and Missouri rivers. Unlike photos taken from planes, this method can show the aerial extent of surface water over a broad region, according to scientists with the National Oceanic and Atmospheric Administration (NOAA) in Camp Springs, Md.

To produce these images, NOAA meteorologist Rao Achutuni and his colleagues mapped data collected by microwave-sensing instruments on several Defense Department satellites. Because water emits less microwave radiation than dry ground does, the satellite information can distinguish soil moisture and flooded regions. Shades of green, orange, and red indicate progressively wetter soil, while flooded land and lakes appear in blue. The experimental technique cannot determine the depth of the water, so deep lakes and shallow puddles appear the same on the images. However, by combining images from several days, the scientists can discriminate between true flooding and temporary puddles that follow rain.

Because the satellite sensors have a resolution of 50 kilometers, they cannot distinguish individual rivers. They can, however, measure soil moisture in overcast conditions, because microwave radiation passes through clouds.

Achutuni and his co-workers are currently testing the technique to determine its accuracy. NOAA's Norman Grody says the system does best at sensing flooded regions, adding that it has a difficult time measuring soil wetness in land covered by crops or other vegetation.
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Title Annotation:National Oceanic and Atmospheric Administration uses new method to show extent of surface wetness over entire Midwest region
Publication:Science News
Article Type:Brief Article
Date:Jul 24, 1993
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